Md. Rabiul Karim

The effect of terminal substituents on crystal structure, mesophase behaviour and optical property of azo-ester linked materials

ABSTRACT A series of azo-ester linked mesogen containing liquid crystalline acrylate compounds C1-C6 having different terminal groups (–F, –Cl, –Br, –OCH3, –OC2H5 and –OC3H7) were successfully synthesised and characterised. The chemical structure, purity, thermal stability, mesophase behaviour and optical property of the synthesised compounds were investigated by different instrumental techniques. X-ray crystal structure showed that compounds C1, C4 and C5 exhibited more stable E configuration with two bulky group in the opposite side of the N=N double bond motifs. The fluoro-substituted derivative (C1) is connected by the R12(5) type of C–H…O hydrogen bond motifs whereas the molecules of C4, and C5 are connected to each other by means cyclic R22(8) type of C–H…O hydrogen bond motifs. Thermogravimetric study revealed that the investigated compounds exhibited excellent thermal stability. All the compounds showed enantiotropic liquid crystal (LC) phase behaviour and the mesophase formation was greatly influenced by the terminal substituents. Alkoxy (–OCH3, –OC2H5 and –OC3H7) substituted compounds exhibited greater mesophase stability than those of halogen (–F, –Cl and –Br) terminated derivatives. UV-vis spectroscopic study revealed that the investigated compounds exhibited a broad absorption band around 300–420 nm with absorption maximum (λmax) of nearly 370 nm. GRAPHICAL ABSTRACT

Mixture models for analyzing product reliability data: a case study

In the case of manufactured products, there are situations where some components of a product are produced over a period of time by collecting items from different vendors, using different raw materials, machines, and manpower. The physical characteristics and the reliabilities of such components may be different, but sometimes it is difficult to distinguish them clearly. In such situations, mixtures of distributions are often used in the analysis of reliability data for these components. Here a twofold Weibull–Weibull mixture model is applied to analyze product reliability data that consist of both failure and censored lifetimes. The Expectation–Maximization (EM) algorithm is used to find the maximum likelihood estimates of the model parameters. As a case study, it analyses an Aircraft component (Windshield) failure data and various characteristics of the mixture model, such as the reliability function, B10 life, mean time to failure, etc., are estimated to assess the reliability of the component. Simulation studies are performed to investigate the properties and uses of the proposed method.

Triethyl­ammonium bis­(2-oxido-2,2-diphenyl­acetato-κ2O1,O2)anti­monate(III)

The coordination around the Sb atom in the title compound, (C6H16N)[Sb(C14H10O3)2], is fourfold in a pseudo-trigonal-bipyramidal pattern in which one of the equatorial sites is occupied by the stereoactive lone pair of electrons. The four ligating atoms comprise the hydoxylate and carboxylate O atoms from two independent benzilate ligands, each of which forms a five-membered chelating ring, spanning an axial and an equatorial site about the Sb atom. The hydroxylate atoms occupy the two equatorial sites, and the carboxylate atoms are in the pseudo-axial sites; the O—Sb—O angle is 147.72 (5)°. One carboxylate group shows quite different bond lengths from those of the other group; one O atom is clearly the carbonyl atom and the other O atom the hydroxylate atom. In the other ligand, there is less distinction in the C—O bonds. This is presumably related to the carbonyl O atom being the acceptor atom of a strong N—H⋯O hydrogen bond, which links the ammonium cation to the Sb complex anion.

Synthesis of imine-ester-linked benzothiazole mesogen containing liquid crystalline monomers with different terminal substituents

ABSTRACT A series of imine-ester-linked benzothiazole mesogen-based liquid crystalline (LC) monomers (M1–M4) having polymerizable methacrylate functional group as the terminal were designed and synthesized. These monomers were differentiated from each other by varying the terminal substituents (-H, -CH3, -OCH3, and -OCH2CH3) at the sixth position on the benzothiazole moiety. The chemical structures of the synthesized monomers were characterized and confirmed by spectroscopic techniques such as FTIR, 1H NMR, and 13C NMR. Thermogravimetric analysis (TGA) was used to study the thermal properties of the investigated monomers. The ethoxy substituted monomer (M4) showed higher thermal stability compared with the other monomers. The mesomorphic behavior of all the monomers was studied using differential scanning calorimetry (DSC) and polarized optical microscopy (POM). DSC and POM studies revealed that the monomer (M1) having no substituent at the sixth position on the benzothiazole ring exhibited both smectic and nematic mesophases, whereas -CH3-, -OCH3-, and -OCH2CH3-substituted compounds revealed only nematic mesophase.

Selecting statistical model and optimum maintenance policy: a case study of hydraulic pump

IntroductionProper maintenance policy can play a vital role for effective investigation of product reliability. Every engineered object such as product, plant or infrastructure needs preventive and corrective maintenance.Case descriptionIn this paper we look at a real case study. It deals with the maintenance of hydraulic pumps used in excavators by a mining company. We obtain the data that the owner had collected and carry out an analysis and building models for pump failures. The data consist of both failure and censored lifetimes of the hydraulic pump.Discussion and evaluationDifferent competitive mixture models are applied to analyze a set of maintenance data of a hydraulic pump. Various characteristics of the mixture models, such as the cumulative distribution function, reliability function, mean time to failure, etc. are estimated to assess the reliability of the pump. Akaike Information Criterion, adjusted Anderson–Darling test statistic, Kolmogrov–Smirnov test statistic and root mean square error are considered to select the suitable models among a set of competitive models. The maximum likelihood estimation method via the EM algorithm is applied mainly for estimating the parameters of the models and reliability related quantities.ConclusionsIn this study, it is found that a threefold mixture model (Weibull–Normal–Exponential) fits well for the hydraulic pump failures data set. This paper also illustrates how a suitable statistical model can be applied to estimate the optimum maintenance period at a minimum cost of a hydraulic pump.